A normal, healthy, heart beats at a regular rate. Irregular heart beats, known as cardiac arrhythmia, on the other hand, may characterize an unhealthy condition. Another unhealthy condition is known as congestive heart failure (ACHF@). CHF, also known as heart failure, is a condition where the heart has inadequate capacity to pump sufficient blood to meet metabolic demand. CHF may be caused by a variety of sources, including, coronary artery disease, myocardial infarction, high blood pressure, heart valve disease, cardiomyopathy, congenital heart disease, endocarditis, myocarditis, and others.
Unhealthy heart conditions may be treated using a cardiac rhythm management (CRM) system. Examples of CRM systems, or pulse generator systems, include defibrillators (including implantable cardioverter defibrillator), pacemakers and other cardiac resynchronization devices.
Typically, a pulse generator is surgically implanted under the skin, but outside the thorax of a patient and includes one or more conductive lead wires that deliver an electrical pulse to the heart according to a therapy schedule. The electrical pulses may be delivered on a predetermined schedule, on an as needed basis, or according to other predetermined criteria.
In some cases, the operation of the pulse generator may be adjusted using an external programmer. The programmer allows a physician to tailor the performance of the pulse generator without performing surgery on the patient. The programmer may communicate with the pulse generator by wireless technology such as radio frequency communication.
A typical programmer includes a wand coupled to a desktop unit by a flexible electrical cord. In use, the operator positions the wand near the implanted device and a signal from the programmer is wirelessly transmitted to the device. Data is extracted from the transmitted signal and stored in internal memory within the implanted device. The implanted device then delivers therapy according to the memory contents. The memory contents may include operating parameters or programming. For example, the implanted device may be wirelessly programmed to deliver electrical shocks at a greater amplitude or with greater frequency.
The ability to wirelessly program an implantable device has taxed the performance and capacity of device data storage and the device power supply and also compelled the addition of a transceiver suitable for communicating with the programmer. To address these needs, some manufacturers have adapted their devices to include additional circuitry as well as increased battery capacity. To the chagrin of the patient, such improvements have, in some instances, resulted in larger case sizes for the implantable device.
Consumer, and therefore, manufacturers, of implanted medical devices have demonstrated a clear desire for, among other things, reduced device size, increased functionality, and increased reliability and longevity. Efforts to provide increased functionality and increased reliability have tended to frustrate the objective of reduced device size. Thus, there is a need for an implanted device with reduced size and yet permits field programmability along with increased reliability.
At initial implantation, the medical device is programmed to provide therapy based on known parameters and conditions of the patient. Follow-up programming of the implanted device, which may take place at a doctor's office, may be based on stored data and patient input. However, for many patients, follow-up visits are infrequent and thus, patients are unable to provide their physician with accurate or complete information regarding the events surrounding a particular cardiac event. For example, few patients are able to provide reliable data concerning their dietary intake just prior to a period of increased heart rate that may have occurred three weeks ago. Thus, there is a need for collecting timely patient data with improved accuracy.